TABLE 1

Agonist potencies and efficacies of HIS and AIPGs at hH₂R-G_sαS and gpH₂R-G_sαS in the GTPase assay

Steady-state GTPase activity in Sf9 membranes expressing hH₂R-G_sαS and gpH₂R-G_sαS was determined as described under Materials and Methods. Reaction mixtures contained ligands at concentrations from 1 nM to 100 μM as appropriate to generate saturated concentration/response curves. Data were analyzed by nonlinear regression and were best fit to sigmoid concentration/response curves. Typical basal GTPase activities ranged between ∼1.5 and 3.0 pmol/mg/min, and the maximal stimulatory effect of histamine (100 μM) amounted to 250 to 350% above basal. The efficacy (E_max) of histamine was determined by nonlinear regression and was set to 1.00. The E_max values of other agonists were referred to this value. Data shown are the means ± S.D. of five to eight experiments performed in duplicates each. The relative potency of histamine was set to 100, and the potencies of other agonists were referred to this value. We also calculated the ratio of the EC₅₀ values of H₂R agonists for hH₂R-G_sαS and gpH₂R-G_sαS.